Network Administration: Top-Level Domains
A top-level domain appears immediately beneath the root domain. Top-level domains come in two categories: generic domains and geographic domains. These categories are described in the following sections.
Generic domains are the popular top-level domains that you see most often on the Internet. Originally, seven top-level organizational domains existed. In 2002, seven more were added to help ease the congestion of the original seven — in particular, the com domain.
The following table summarizes the original seven generic top-level domains. Of these, you can see that the com domain is far and away the most populated, with nearly 1.9 million second-level domains beneath it.
The Size column in this table indicates approximately how many second-level domains existed under each top-level domain as of January 2007, according to an Internet Software Consortium survey.
|gov||U.S. government institutions||966|
|int||International treaty organizations||119|
|mil||U.S. military institutions||110|
Because the com domain ballooned to an almost unmanageable size in the late 1990s, the Internet authorities approved seven new top-level domains in an effort to take some of the heat off of the com domain. Most of these domains, listed in the following table, became available in 2002. As you can see, they haven’t really caught on yet even though they’ve been around for several years.
Although the top-level domains are open to anyone, U.S. companies and organizations dominate them. An additional set of top-level domains corresponds to international country designations. Organizations outside the United States often use these top-level domains to avoid the congestion of the generic domains.
The following table lists those geographic top-level domains with more than 200 registered subdomains at the time of this writing, in alphabetical order. In all, about 150 geographic top-level domains exist. The exact number varies from time to time as political circumstances change.
|ae||United Arab Emirates||ie||Ireland|
|ag||Antigua and Barbuda||in||India|
|be||Belgium||la||Lao People’s Democratic Republic|
|cc||Cocos (Keeling) Islands||ma||Morocco|
|fi||Finland||st||Sao Tome and Principe|